如何將 MySQL 查詢轉換為 PDO 準備語句並取得結果？

如何將 MySQL 程式碼轉換為 PDO 語句？

需求

我需要將第一個 if 語句改為 PDO 語句，但我不知道該怎麼做。請有人幫忙嗎？

當使用者提交表單時，我希望使用註冊時分配的編號$id 將他們的電子郵件地址從資料庫上的使用者表中提取到網站上的此頁面中.

解決方案

建立連接

首先，您需要將mysqli 連接替換為PDO 連接（或至少在旁邊添加PDO 連接） mysqli 那個！ ）。

// Define database connection parameters
$db_host = "127.0.0.1";
$db_name = "name_of_database";
$db_user = "user_name";
$db_pass = "user_password";


// Create a connection to the MySQL database using PDO
$pdo = new pdo(
    "mysql:host={$db_host};dbname={$db_name}",
    $db_user,
    $db_pass,
    [
        PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
        PDO::ATTR_EMULATE_PREPARES => FALSE
    ]
);

更新你的程式碼

使用mysqli 和PDO 準備的語句

差不多了將變數資料放了入SQL 查詢時，最好使用準備好的語句。它不僅更安全（如果資料來自任何類型的使用者產生的輸入），而且還使其更易於閱讀，並且更易於使用不同的值多次運行。

使用mysqli 準備查詢:

$sql   = "SELECT column1, column2 FROM table WHERE column3 = ? AND column4 = ?";
$query = $mysqli->prepare($sql);
$query->bind_param("si", $string_condition, $int_condition);
$query->execute();
$query->store_result();
$query->bind_result($column1, $column2);
$query->fetch();

echo "Column1: {$column1}<br>";
echo "Column2: {$column2}";

使用PDO 準備查詢:

$sql   = "SELECT column1, column2 FROM table WHERE column3 = ? AND column4 = ?";
$query = $pdo->prepare($sql);
$query->execute([$string_condition, $int_condition]);
$row   = $query->fetchObject();
# $row = $query->fetch(); // Alternative to get indexed and/or associative array

echo "Column1: {$row->column1}<br>";
echo "Column2: {$row->column2}";

的程式碼

// Using the NULL coalescing operator here is shorter than a ternary
$id = $_SESSION['u_id'] ?? NULL;

if($id) {
    $sql   = "SELECT email FROM users WHERE u_id = ?";
    $query = $pdo->prepare($sql);    // Prepare the query
    $query->execute([$id]);          // Bind the parameter and execute the query
    $email = $query->fetchColumn();  // Return the value from the database
}

// Putting "$email" on a line by itself does nothing for your code. The only
// thing it does is generate a "Notice" if it hasn't been defined earlier in
// the code. Best use:
//    - The ternary operator: $email = (isset($email)) ? $email : "";
//    - The NULL coalescing operator: $email = $email ?? "";
//    - OR initialize it earlier in code, before the first `if`, like: $email = "";
// N.B. Instead of "" you could use NULL or FALSE as well. Basically in this case 
//    anything that equates to BOOL(FALSE); so we can use them in `if` statements
//    so the following (2 commented lines and 1 uncommented) are effectively
//    interchangeable.
$email = $email ?? "";
# $email = $email ?? FALSE; 
# $email = $email ?? NULL;

// Presumably you will also want to change this function to PDO and prepared statements?
// Although it doesn't actually do anything in the code provided?
$suggestions = selectAll($table);  

// Same as with email, we're just going to use the NULL coalescing operator.
// Note: in this case you had used the third option from above - I've just
//   changed it so there is less bloat.
$optionOne     = $_POST['optionOne'] ?? "";
$optionTwo     = $_POST['optionTwo'] ?? "";
$newSuggestion = $_POST['new-suggestion'] ?? "";

// There's no point nesting `if` statements like this when there doesn't appear to be any
// additional code executed based on the out come of each statement? Just put it into one.
// We now don't need to use empty etc. because an empty, false, or null string all.
// equate to FALSE.
if($newSuggestion && $id && $email && $optionOne && $optionTwo) {
    // Not sure why you've made the the table name a variable UNLESS you have multiple tables
    // with exactly the same columns etc. and need to place in different ones at different
    // times. Which seems unlikely so I've just put the table name inline.
    $sql   = "INSERT INTO suggestions (user_id, email, option_1, option_2) VALUES (?, ?, ?, ?)";
    $query = $pdo->prepare($sql);
    $query->execute([$id, $email, $optionOne, $optionTwo]);
}
else{
    echo "All options must be entered";
}

沒有註解：

$id = $_SESSION['u_id'] ?? NULL;

if($id) {
    $sql   = "SELECT email FROM users WHERE u_id = ?";
    $query = $pdo->prepare($sql);
    $query->execute([$id]);
    $email = $query->fetchColumn();
}
$email       = $email ?? "";
$suggestions = selectAll($table);  

$optionOne     = $_POST['optionOne'] ?? "";
$optionTwo     = $_POST['optionTwo'] ?? "";
$newSuggestion = $_POST['new-suggestion'] ?? "";

if($newSuggestion && $id && $email && $optionOne && $optionTwo) {
    $sql   = "INSERT INTO suggestions (user_id, email, option_1, option_2) VALUES (?, ?, ?, ?)";
    $query = $pdo->prepare($sql);
    $query->execute([$id, $email, $optionOne, $optionTwo]);
}
else{
    echo "All options must be entered";
}

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